Advanced signal processors for interference cancellation in baseband receivers

ABSTRACT

An interference canceller comprises a composite interference vector (CIV) generator configured to produce a CIV by combining soft and/or hard estimates of interference, an interference-cancelling operator configured for generating a soft projection operator, and a soft-projection canceller configured for performing a soft projection of the received baseband signal to output an interference-cancelled signal. Weights used in the soft-projection operator are selected to maximize a post-processing SINR.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/272,411, entitled “Variable interference cancellation technology forCDMA systems,” filed Nov. 10, 2005, now U.S. Pat. No. 7,808,937, which(1) is a continuation-in-part of U.S. patent application Ser. No.11/233,636, entitled “Optimal feedback weighting for soft-decisioncancellers,” filed Sep. 23, 2005 and published as U.S. PatentApplication Publication Number 2006-0227909 A1; and (2) is acontinuation-in-part of U.S. patent application Ser. No. 11/100,935,entitled “Construction of Projection Operators for InterferenceCancellation,” filed Apr. 7, 2005, and published as U.S. PatentApplication Publication Number 2005-0180364 A1, which is acontinuation-in-part of U.S. patent application Ser. No. 10/773,777,entitled “Systems and Methods for Parallel Signal Cancellation,” filedFeb. 6, 2004, now U.S. Pat. No. 7,394,879; which is acontinuation-in-part of (a) U.S. patent application Ser. No. 10/686,359,entitled “System and Method for Adjusting Phase,” filed Oct. 15, 2003,now U.S. Pat. No. 7,068,706; (b) U.S. patent application Ser. No.10/686,829, entitled “Method and Apparatus for Channel AmplitudeEstimation and Interference Vector Construction,” filed Oct. 15, 2003,now U.S. Pat. No. 7,580,448; (c) U.S. patent application Ser. No.10/294,834, entitled “Construction of an Interference Matrix for a CodedSignal Processing Engine,” filed Nov. 15, 2002, now U.S. Pat. No.7,200,183; and (d) U.S. patent application Ser. No. 10/247,836, entitled“Serial Cancellation Receiver Design for a Coded Signal ProcessingEngine,” filed Sep. 20, 2002, now U.S. Pat. No. 7,158,559. The entiretyof each of the foregoing patents, patent applications, and patentapplication publications is incorporated by reference herein.

BACKGROUND

1. Field of the Invention

The present invention relates generally to interference cancellation inreceived wireless communication signals and, more particularly, toforming and using a composite interference signal for interferencecancellation.

2. Discussion of the Related Art

In an exemplary wireless multiple-access system, a communicationresource is divided into subchannels and allocated to different users.For example, subchannels may include time slots, frequency slots,multiple-access codes, spatio-temporal subchannels, or any combinationthereof. A plurality of sub-channel signals received by a wirelessterminal (e.g., a subscriber unit or a base station) may correspond todifferent users and/or different subchannels allocated to a particularuser.

If a single transmitter broadcasts different messages to differentreceivers, such as a base station in a wireless communication systembroadcasting to a plurality of mobile terminals, the channel resource issubdivided in order to distinguish between messages intended for eachmobile. Thus, each mobile terminal, by knowing its allocatedsubchannel(s), may decode messages intended for it from thesuperposition of received signals. Similarly, a base station typicallyseparates signals it receives into subchannels in order to differentiatebetween users.

In a multipath environment, received signals are superpositions of timedelayed (and complex scaled) versions of the transmitted signals.Multipath can cause co-channel and cross-channel interference thatcorrelates the allocated subchannels. For example, co-channelinterference may occur when time-delayed reflections of transmittedsignals from the same source interfere with each other. Cross-channelinterference occurs when signals in a sub channel leak into and, thus,impair acquisition and tracking of other subchannels.

Co-channel and cross-channel interference can degrade communications bycausing a receiver to incorrectly decode received transmissions, thusincreasing a receiver's error floor. Interference may also have otherdegrading effects on communications. For example, uncancelledinterference may diminish capacity of a communication system, decreasethe region of coverage, and/or decrease maximum data rates. Previousinterference-cancellation techniques include subtractive and projectiveinterference cancellation, such as disclosed in U.S. Pat. Nos. 6,856,945and 6,947,474, which are hereby incorporated by reference.

SUMMARY OF THE INVENTION

In view of the foregoing background, embodiments of the presentinvention may be employed in receivers configured to implement receivediversity and equalization. Embodiments may provide for optimallyforming and using at least one composite interference vector (CIV) foruse in any subtractive or projective interference canceller. Suchembodiments may be employed in any receiver employing a Rake, such as(but not limited to) receivers configured to receive ultra-wideband(UWB), Code Division Multiple Access (CDMA),Multiple-Input/Multiple-Output (MIMO), and narrowband single-carriersignals. Embodiments of the invention may provide for analyticallycharacterizing the signal-to-interference-and-noise ratio (SINR) in acomposite signal or in a user subchannel, and choosing feedback terms(e.g., adaptive weights) to construct an interference-cancelled signalthat maximizes this quantity.

Embodiments of the invention employ soft weighting of a projectiveoperation to improve interference cancellation. For example, each fingerof a Rake receiver is matched to a particular time delay and/or basestation spreading code to combat the effects of frequency-selectivefading and interference from multiple base stations, respectively.Inter-finger interference occurs due to loss of orthogonality in theuser waveforms resulting from multi paths in the transmission channel.This interference may be mitigated by feeding soft estimates of activeusers' waveforms between the Rake fingers in order to improve the SINRat the output of each finger. The optimization is performed per Rakefinger prior to combining. In a receiver employing receive diversity,fingers that are common to two or more receive paths may be combinedusing any of various well-known statistical signal-processingtechniques.

In one embodiment of the invention, a means for generating one or moreCIVs, a means for generating a soft-projection operator, and a means forperforming a soft projection are configured to produce aninterference-cancelled signal from a received baseband signal. The meansfor generating the one or more CIVs may include, by way of example, anymeans for deriving soft and/or hard estimates from a receiver andsynthesizing the one or more CIVs therefrom. For example, the means forgenerating the one or more CIVs may include a symbol estimator (e.g., asymbol estimator in a receiver employing any combination of Rakeprocessing, receive diversity, and equalization), a sub channelselector, a fast Walsh transform, and a PN coder. The means forgenerating the one or more CIVs may further include a channel emulator.The means for generating a soft-projection operator may include, by wayof example, a soft-projection matrix generator or aninterference-cancelling operator that includes a means for selecting asoft weight that maximizes a post-processing SINR. The means forperforming a soft projection may include, by way of example, a signalprocessor configured to project a received baseband signal as specifiedby the soft-projection operator in order to produce aninterference-cancelled signal.

Receivers and cancellation systems described herein may be employed insubscriber-side devices (e.g., cellular handsets, wireless modems, andconsumer premises equipment) and/or server-side devices (e.g., cellularbase stations, wireless access points, wireless routers, wirelessrelays, and repeaters). Chipsets for subscriber-side and/or server-sidedevices may be configured to perform at least some of the receiverand/or cancellation functionality of the embodiments described herein.

Various functional elements, separately or in combination, depicted inthe figures may take the form of a microprocessor, digital signalprocessor, application specific integrated circuit, field programmablegate array, or other logic circuitry programmed or otherwise configuredto operate as described herein. Accordingly, embodiments may take theform of programmable features executed by a common processor or discretehardware unit.

These and other embodiments of the invention are described with respectto the figures and the following description of the preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments according to the present invention are understood withreference to the flow diagram of FIG. 1 and the schematic block diagramsof FIGS. 2A and 2B.

FIG. 1 is a flow diagram of an interference-cancelling method for aparticular multipath component.

FIG. 2A is a schematic block diagram of a circuit configured forcancelling interference and combining interference-cancelled multipathcomponents.

FIG. 2B is a schematic block diagram of a circuit configured forcancelling interference from at least one finger of a Rake receiver thatproduces a CIV from signals received by all fingers of the Rakereceiver.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

A received baseband signal at a user handset having K base stations (orsubchannels), U users, L propagation paths, and a sequence oftransmitted symbols {b_(k)[m]} can be expressed by

${y\lbrack n\rbrack} = {{\sum\limits_{k = 1}^{K}{\sum\limits_{m = {- \infty}}^{\infty}{\sum\limits_{l = 1}^{L}{c_{k,l}{s_{k}\left\lbrack {{n - {Nm} - d_{k,l}},{b_{k}\lbrack m\rbrack}} \right\rbrack}}}}} + {v\lbrack n\rbrack}}$where {s_(k)[n, b_(k)[m]]} is a discrete-time symbol-bearing waveformfrom base station k that has N samples per symbol period, the vectorsequence {b_(k)[m]} is a sequence of U user information symbolsb_(k)[m]=[b_(k,1)[m], . . . , b_(k,U)[m]] from base station k, thevalues C_(k,1) and d_(k,l) are the complex channel fading coefficientsand the time delays characterizing the propagation channel linking thek^(th) base station to the receiver, and ν[n] is additive noise havingpower σ². When a multi-code (e.g., CDMA, DSSS, WCDMA, DO) transmissionis employed, a transmitted waveform can be represented as

${{s_{k}\left\lbrack {n,{b_{k}\lbrack m\rbrack}} \right\rbrack} = {\sum\limits_{u = 1}^{U}{{b_{k,u}\lbrack m\rbrack}{w_{k,u}\lbrack n\rbrack}}}},{{mN} \leq n < {\left( {m + 1} \right)N}}$where U is the number of users, b_(k,u)[m] is a user data symbol (whichis drawn from a finite constellation and is constant over symbolintervals of sample length N), and w_(k,u)[n] is a user spreading code(including PN, covering, and filtering), which is typically time varyingat the sample rate. The sampling rate corresponding to n is taken to bethe normalized rate 1 and assumed to be greater than the chip rate. Thereceived signal y[n] may be organized into a sequence of vectors at rate1/N

${\left. {{y\lbrack m\rbrack} = {\sum\limits_{k = 1}^{K}{\sum\limits_{m^{\prime}}{\sum\limits_{l}^{L}{c_{k,l}{w_{k,l}\left\lbrack {m - m^{\prime}} \right\rbrack}{b_{k}\left\lbrack m^{\prime} \right\rbrack}}}}}} \right\rbrack + {v\lbrack m\rbrack}},$where b_(k) contains symbols b_(k,u) and the columns of the matrixW_(k,l) comprise vectors of the formw _(k,l,u) =[w _(k,l,u) [mN−d _(l) ], . . . , w _(k,l,u)[(m+1)N−1−d_(l)]]^(T)Thus, the sampling rate corresponding to m remains 1/N.

The optimal receiver for a given user information sequence depends onthe cellular network's operating mode (e.g., soft handoff, blocking).For example, if a particular handset is not in handoff and there is nointer-base-station interference (i.e., K=1), the optimal detectionstrategy for a single symbol of interest corresponding to a designateduser is

${b_{u}\lbrack m\rbrack} = {\arg\mspace{11mu}{\max\limits_{b}\mspace{11mu}{\max\limits_{{{\{{b_{u^{\prime}}{\lbrack m^{\prime}\rbrack}}\}}:{b_{u}{\lbrack m\rbrack}}} = b}{{Re}{\sum\limits_{l}{{\overset{\_}{c}}_{l}{s_{l}^{*}\left\lbrack {m;\left\{ {b\left\lbrack m^{\prime} \right\rbrack} \right\}} \right\rbrack}\left( {{y\lbrack m\rbrack} - {\frac{1}{2}{s\left\lbrack {{m;\left\{ {b\left\lbrack m^{\prime} \right\rbrack} \right\}},l} \right\rbrack}}} \right)}}}}}}$where overbar denotes a complex conjugate and superscript * denotes aHermitian transpose. The term s_(l)[m; {b[m′]}] is a received signalvector, delayed by d_(l) corresponding to the vector-valued informationsequence {b[m′]}, and the vector

${{s\left\lbrack {{m;\left\{ {b\left\lbrack m^{\prime} \right\rbrack} \right\}},l} \right\rbrack} = {\sum\limits_{l^{\prime} \neq l}c_{l}}},s_{l},\left\lbrack {m;\left\{ {b\left\lbrack m^{\prime} \right\rbrack} \right\}} \right\rbrack$represents an interference signal formed from all of the paths not equalto path l. This exemplary embodiment impels approximations that cancelinterference terms s_(l)[m; {b[m′}] from received signals, in advance ofRake reception (i.e., the sum over l of c_(l)s_(l)[m]. The vectors_(l)[m; {b[m′]}] may be expressed ass _(l) [m;{b[m′]}]=[s[mN−d _(l) ,{b[m]}], . . . , s[(m+1)N−1−d _(l),{b[m′]}]]

When the complex baseband signal y[m] is resolved at a particular(l^(h)) finger in a handset's Rake receiver, it can be simplified to avector representationy=cx _(u) b _(u) +x _(MAI) +X _(INT) +vwhere y represents received data after it passes through a receiverpulse-shaping filter (e.g., a root raised-cosine pulse-shaping filter).The data y is time aligned to a particular path delay. The term c is acomplex attenuation corresponding to the path.

When the modulation is linear, the term x_(u) in path l, whichrepresents a code waveform that typically includes an orthogonal basiscode and an overlaid spreading sequence (e.g., a PN code) assigned to auser of interest, may be written asx _(1,l,u) [m]=c _(1,l) w _(1,l,u) b _(1,u) [m]The term W_(1,u), is the spread and scrambled code for user u in cellk=1, and b_(1,u), is an information symbol corresponding to the user ofinterest. The term x_(MAI) is multiple access interference, and it maybe expressed by

${x_{1,l,{MAI}}\lbrack m\rbrack} = {c_{l}{\sum\limits_{u^{\prime} \neq u}{w_{1,l,u}{{b_{1,u}\lbrack m\rbrack}.}}}}$The term x_(INT) may include inter-finger (and possiblyinter-base-station) interference terms that are similar in form tox_(MAI). The term v is a vector of complex additive noise terms. Each ofthe vectors x_(u), x_(MAI) and x_(INT) is a signal resolved onto a Rakefinger matched to the l^(th) multipath delay of base station k at symbolperiod m.

A conventional Rake receiver resolves the measurement x_(u) onto auser's code vector to form the statistic x_(u)*y_(l). Such statisticsare typically derived from multiple Rake fingers and coherently combinedacross the paths via a maximum ratio combiner (i.e. they are weighted bythe conjugate of the channel gains and summed). Alternatively, moregeneral combining may be used.

FIG. 1 illustrates a signal processing method in accordance with anexemplary embodiment of the invention that is configured to reduce ISIin a received signal from a particular Rake finger. A CIV s is generated101 by combining soft or hard estimates of interference corresponding tothe other delays and/or base stations not tracked by the particularfinger. For example, the soft estimates may correspond to interferinguser subchannels from each base station tracked by a cellular handset.Soft or hard estimates may be derived from a conventional Rake receiver,an equalizer, or any detector matched to the communication protocol andchannel conditions of a received signal. Embodiments of the inventionmay be configurable to operate within receivers employing receivediversity, equalization, transmit diversity combining, and/or space-timedecoding.

Embodiments of the invention may include one or more CIVs. Therefore, inparts of the disclosure that describe a CIV, it is anticipated that aplurality of CIVs may be used. For example, specific embodiments mayemploy a matrix whose columns are CIVs. The CIV s is constructed fromknown and/or estimated active subchannels and then used to compute asoft projection matrix 102,F(λ)=I−λss*.

The matrix F(λ) is configured to operate on a received data vector y 103to produce an interference-cancelled signal ŷ=F(λ)y, which is coupled toa Rake processor or combiner (not shown). The term I is an identitymatrix, and the weight λ may be determined symbol-by-symbol in order tomaximize a post-processing SINR,

${\Gamma(\lambda)} = \frac{{{x_{u}^{*}{F(\lambda)}x_{u}}}^{2}}{{E{{x_{u}^{*}{F(\lambda)}x_{MAI}}}^{2}} + {E{{x_{u}^{*}{F(\lambda)}x_{INT}}}^{2}} + {\sigma^{2}x_{u}^{*}{F(\lambda)}{F^{*}(\lambda)}x_{u}}}$In this expression, each vector of the form x_(u) is x_(u)[m],corresponding to symbol period m. Therefore, the post-processing SINRΓ(λ) is measured symbol period-by-symbol period. The user powers areabsorbed into the component vectors x_(u), x_(MAI), and x_(INT). Thesepowers are known or estimated.

At each symbol period, the SINR at a given finger can be expressed as

${\Gamma(\lambda)} = \frac{a + {b\;\lambda} + {c\;\lambda^{2}}}{d + {e\;\lambda} + {f\;\lambda^{2}}}$The coefficients are

$\begin{matrix}{a = {{x_{u}^{*}x_{u}}}^{2}} \\{b = {{- 2}x_{u}^{*}x_{u}{{x_{u}^{*}s}}^{2}}} \\{c = {{x_{u}^{*}s}}^{4}} \\{d = {{\sum\limits_{u^{\prime} \neq u}{{x_{u}^{*}x_{u^{\prime}}}}^{2}} + {{x_{u}^{*}s}}^{2} + {\sigma^{2}x_{u}^{*}x_{u}}}} \\{e = {{- 2}\;{{Re}\left( {{\sum\limits_{u^{\prime} \neq u}{\left( {x_{u}^{*}x_{u^{\prime}}} \right)\left( {x_{u}^{*}s} \right)\left( {s^{*}x_{u^{\prime}}} \right)}} + {{{x_{u}^{*}s}}^{2}s^{*}s} + {\sigma^{2}{{x_{u}^{*}s}}^{2}}} \right)}}} \\{f = {{\sum\limits_{u^{\prime} \neq u}{{{x_{u}^{*}s}}^{2}{{s^{*}x_{u^{\prime}}}}^{2}}} + {{{x_{u}^{*}s}}^{2}{{s^{*}s}}^{2}} + {\sigma^{2}{{x_{u}^{*}s}}^{2}\left( {s^{*}s} \right)}}}\end{matrix}$wherein each of the inner products may be computed from the user codesw_(k)[m] and complex amplitudes b_(l,u)[m] identified for user u at baudinterval m. If orthogonal spreading codes are used, the expressionx_(u)*x_(u) with u′ ≠u is zero. Furthermore, the relevant inner productx_(u)*s can be efficiently obtained for a CDMA/WCDMA system by passingthe synthesized CIV s for the finger of interest through a fast Walshtransform (FWT). Computing the soft projection matrix 102 may include astep of maximizing the SINR Γ(λ) by setting its derivative (with respectto λ) to zero (not shown), resulting in the following polynomialequation(ce−bf)λ²+2(cd−af)λ+(bd−ae)=0.One of the roots of the polynomial equation corresponding to the maximumSINR is selected (not shown) and then used to scale ss* in the matrixF(λ). Once computed, F(λ)y may be scaled to conform to downstreamprocessing in a baseband receiver.

It should be appreciated that variations to the previously describedprocess for determining the weight λ may be made without departing fromthe spirit and scope of the claimed invention. For example, when acellular handset is in a soft-handoff mode, there is an additionalquadratic term in the numerator of Γ(λ) corresponding to the receivedsignal power from the second base station, and there is one less term inthe denominator. This changes the function Γ(λ), but it does not changethe procedure for determining the value of Γ(λ) that maximizes Γ(λ).Furthermore, algorithms for maximizing Γ(λ) may be incorporated intoother receiver processing techniques, such as (but not limited to) Rakepath tracking, active user determination, amplitude estimation, receivediversity, and equalizing. Γ(λ) may be approximately maximized withvariations or stochastic gradients.

FIG. 2A is a schematic block diagram of a circuit in accordance with analternative embodiment of the invention that includes a CIV generator201, an interference-cancelling operator 202, and a soft-projectioncanceller 203. Inputs to the CIV generator 201 and the soft-projectioncanceller 203 are coupled to outputs of a Rake receiver 200. An outputof the soft-projection canceller 203 is coupled to the input of acombiner 210.

The soft-projection canceller 203 is configured to cancel interferencefrom at least one path (or finger) of the Rake receiver 200. Soft and/orhard estimates from at least one other path or finger are processed bythe CIV generator 201 to produce a CIV s. For example, FIG. 2B showssignals from rake fingers 210.1-210.N being used to construct a CIV inorder to cancel interference from one of the rake fingers (e.g., 210.1).The interference-cancelling operator 202 uses the CIV s and user codex_(u) to compute a soft-projection matrix. The soft-projection matrixcomputes the weight value λ that maximizes the SINR of theinterference-cancelled signal ŷ=F(λ)y. The interference-cancelled signalŷ output from the soft-projection canceller 203 may be coupled into thecombiner 210 and combined with interference-cancelled signals from otherpaths or Rake fingers.

The functions of the various elements shown in the drawings, includingfunctional blocks, may be provided through the use of dedicatedhardware, as well as hardware capable of executing software inassociation with appropriate software. When provided by a processor, thefunctions may be performed by a single dedicated processor, by a sharedprocessor, or by a plurality of individual processors, some of which maybe shared. Moreover, explicit use of the term “processor” should not beconstrued to refer exclusively to hardware capable of executingsoftware, and may implicitly include, without limitation, digital signalprocessor DSP hardware, read-only memory (ROM) for storing software,random access memory (RAM), and non-volatile storage. Other hardware,conventional and/or custom, may also be included. Similarly, thefunction of any component or device described herein may be carried outthrough the operation of program logic, through dedicated logic, throughthe interaction of program control and dedicated logic, or evenmanually, the particular technique being selectable by the implementeras more specifically understood from the context.

The method and system embodiments described herein merely illustrateparticular embodiments of the invention. It should be appreciated thatthose skilled in the art will be able to devise various arrangements,which, although not explicitly described or shown herein, embody theprinciples of the invention and are included within its spirit andscope. Furthermore, all examples and conditional language recited hereinare intended to be only for pedagogical purposes to aid the reader inunderstanding the principles of the invention. This disclosure and itsassociated references are to be construed as applying without limitationto such specifically recited examples and conditions. Moreover, allstatements herein reciting principles, aspects, and embodiments of theinvention, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include currentlyknown equivalents as well as equivalents developed in the future, i.e.,any elements developed that perform the same function, regardless ofstructure.

The invention claimed is:
 1. A method for cancelling interference from areceived baseband signal in a CDMA system, comprising: generating atleast one composite interference vector (CIV) by combining estimatesfrom interfering subchannels, generating a soft-cancellation operator,and performing a soft cancellation of the received baseband signal tooutput an interference-cancelled signal, wherein the estimates arederived from a Rake receiver.
 2. The method recited in claim 1, whereineach finger of the Rake receiver is matched to at least one of a timedelay and a base station spreading code.
 3. The method recited in claim1, wherein generating at least one CIV comprises generating at least oneof soft estimates and hard estimates from the interfering subchannels.4. The method recited in claim 1, wherein generating at least one CIVcomprises generating at least one or more soft estimates correspondingto interfering user subchannels from each base station tracked by acellular handset.
 5. The method recited in claim 1, wherein the at leastone of soft estimates and hard estimates is derived from a selected oneof a Rake receiver, an equalizer, and a detector matched to thecommunication protocol and channel conditions of the received basebandsignal.
 6. The method recited in claim 1, wherein the at least one CIVis generated using at least one of a symbol estimator, a sub channelselector, a fast Walsh transform, and a PN coder.
 7. The method recitedin claim 6, wherein the at least one CIV is generated using a symbolestimator employing at least one of Rake processing, receive diversityand equalization.
 8. The method recited in claim 1, wherein performing asoft cancellation comprises at least one of subtractive and projectiveinterference cancellation.
 9. The method recited in claim 1, wherein thesoft cancellation operator comprises a soft-projection matrix generatoror an interference-cancelling operator configured for selecting a softweight that increases a post-processing SINR.
 10. The method recited inclaim 1, wherein the received baseband signal is coupled to a first Rakefinger and generating the at least one CIV comprises generating the atleast one CIV from at least one Rake finger that does not include thefirst Rake finger.
 11. The method recited in claim 1, wherein generatingthe at least one CIV comprises deriving the estimates from at least oneof a Rake receiver, an equalizer, a receiver employing receivediversity, a receiver employing transmit diversity combining, and areceiver employing space-time decoding.
 12. The method recited in claim1, wherein generating the soft-cancellation operator comprisesgenerating a soft-projection matrix to operate on a received datavector, the soft-projection matrix having the form F(λ)=I−λss*, where Iis an identity matrix, λ is a weight, and s is a CIV.
 13. The methodrecited in claim 12, wherein generating the soft-cancellation operatorcomprises determining the weight λ by maximizing a post-processing SINR.14. The method recited in claim 13, wherein generating thesoft-cancellation operator comprises determining the weight λ bymaximizing a post-processing SINR for a handset operating in asoft-handoff mode.
 15. The method recited in claim 1, wherein performingthe soft cancellation further comprises coupling theinterference-cancelled signal to at least one of a combiner and a Rakereceiver.
 16. The method recited in claim 15, further comprisingcombining a plurality of interference-cancelled signals.
 17. The methodrecited in claim 1, wherein the CDMA system is configured to implementreceive diversity and equalization.